The present invention relates to an apparatus for producing an instantaneous pressure onto a workpiece with a working piston impingable by gas under pressure and a control arrangement constructed to let the gas pressure in a controlled manner to act on the working piston.
A known apparatus of this kind comprises a cylinder which is separated into two chambers by a wall provided with a bore therethrough. A working piston is axially guided in a sealed manner in one of the chambers, whereas a control piston of a control device is arranged in the other chamber, and held by hydraulic pressure in a position closing the bore in the separating wall. The chamber separated from the working piston is impinged by a gas under high pressure. When the necessary working pressure is obtained in the other chamber, the hydraulic pressure acting on the control piston is released so that the latter is moved away from the separating wall and opens thereby the bore therethrough to provide communication between the two chambers. The gas under high pressure expands through the bore in the separating wall and accelerates the working piston to high speed.
A decisive disadvantage of this known apparatus is that the working piston has first to be accelerated to obtain the deforming energy and to impinge with high speed on the workpiece. This requires that the apparatus must be built correspondingly long and heavy. A further disadvantage of this known apparatus is that the highly compressed gas has to pass through the bore in the separating wall in order to act on the working piston, whereby a considerable throttling action will occur which considerably increases the pressure build-up in the working cylinder. In addition, since the working piston, respectively the piston rod thereof, is initially spaced from the workpiece and moves at high speed in engagement therewith, the operation of this known apparatus leads to considerable vibrations thereof and undesirable development of noise.